Load line analysis in femm4.2

In summary, Paul is asking for help with interpreting load-line analysis results for loudspeaker driver magnetic circuits. He is confused by different sources reporting different values for the permeance coefficient. BarMagnet.pdf provides helpful information about calculating the permeance coefficient for random points inside a magnet.
  • #1
flowwolf
27
4
Dear Forumers,

This question is about load-line analysis for loudspeaker driver magnetic circuits in FEMM 4.2 (Finite Element Method for Magnetics), I can't seem to get an answer from the mailing lists.

I would like to get the permeance coefficient for random points inside the magnet.
I have problems interpreting the results reported by femm.
Most information sources tell me that pc = Bd/Hd, but B and H are vector quantities,
and I'm not sure which parts to use (either |B|,|H| or the components).

According to a JMAG newsletter I've read, Pc = - Bd / (µ0 Hd), where
"Bd [T], Hd [A/m]: The projection components in the magnetizing direction M of the magnetic flux density B and magnetic field H"

So does that mean that pc = Bz / Hz, if the magnetization direction is 90 degrees?I saw old mails about the permeance coefficient as well: http://www.femm.info/list/msg01827.html
where it was stated that Hd = H - Hc (if the "Demag. H in PMs" option is not set)

But subtracting Hc from |H| does not result in the |H| that is reported when "Demag. H in PMs" is setAll these confuses me, could I get some help about which values to use?

Also do Bd and Hd necessarily have to fall on the BH curve, or is the load-line given by
the intersection of a line with steepness of pc, where Bd and Hd are not necessarily on the BH curve?Any help would by appreciated.

Akos
 
  • #3
Are the magnetic materials isotropic (same in every direction)? If so the B and H vectors are in the same direction and I would think the magnitudes would be the natural choice. About the load line problem, I'd like to know more about it as I have similar modeling issues with piezoelectric materials. I too find it confusing.
 
  • #4
Hello Paul,
I've received an answer from David Meeker:
"For your case, on a point-by-point basis, you'd want to compute:
Pc = (B.M)/(µ0*H.M)
where B is the reported B for a point inside a PM, H is the reported H for a point in the PM (with the default (checked) "Demag H in PMs" setting), and M is the magnetization in the block. Note that B, H, and M are all vectors, and . represents the dot product."

He pointed me to http://www.femm.info/Archives/misc/BarMagnet.pdf
 
  • Like
Likes Paul Colby
  • #5
Very helpful, thanks. I once analyzed a variable reluctance motor using magnetic circuit theory. The parallel with piezoelectric materials should be understandable.
 

1. What is load line analysis in femm4.2?

Load line analysis in femm4.2 is a numerical method used to analyze the behavior of electrical circuits under varying load conditions. It involves plotting load line curves, which show the relationship between voltage and current in a circuit, and using these curves to determine the operating point of the circuit.

2. How does load line analysis work in femm4.2?

Load line analysis in femm4.2 uses a combination of mathematical equations and graphical representations to analyze the behavior of electrical circuits. It involves solving simultaneous equations to find the intersection point of the load line curve and the characteristic curve of the circuit, which represents the operating point of the circuit.

3. What are the benefits of using femm4.2 for load line analysis?

Femm4.2 is a powerful and user-friendly software that allows for accurate and efficient load line analysis. It provides a comprehensive set of tools for creating, analyzing, and visualizing load line curves, making it a valuable tool for designing and optimizing electrical circuits.

4. What types of circuits can be analyzed using load line analysis in femm4.2?

Load line analysis in femm4.2 can be applied to a wide range of circuits, including linear and nonlinear circuits, DC and AC circuits, and single- and multi-loop circuits. It can also be used to analyze circuits with various types of components, such as resistors, capacitors, and diodes.

5. Are there any limitations to load line analysis in femm4.2?

While femm4.2 is a powerful tool for load line analysis, it does have some limitations. It may not be suitable for analyzing complex circuits with multiple non-linear components or circuits with high-frequency signals. Additionally, the accuracy of the analysis may be affected by factors such as component tolerances and temperature variations.

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